The present invention relates in general to the construction of heat pipes.
A heat pipe is a device for transmitting heat from one location to another with a small temperature gradient. The heat pipe has found varied applications in many fields since the first publication of its operating principles in 1964 by scientists at Los Alamos Scientific Laboratory. The book Heat Pipe Theory and Practice by S.W. Chi, McGraw-Hill 1976, provides information on heat pipes. Sections 1-2 and 1-3 of this reference cover heat pipe working fluids and wick structures, respectively. Section 1-4 is of primary interest for this disclosure since it covers control techniques for heat pipes. As stated in Section 1-4, heat pipes do not have any particular operating temperature. They adjust their temperature according to the heat-source and heat-sink conditions. In many cases, it is desirable to maintain certain portions of the heat pipe at a set temperature range even during variation in the heat-source and heat-sink conditions (variable conductance heat pipes). Major control approaches can be categorized into four classes: (1) condenser blocking with noncondensing gases (gas-loaded heat pipe), (2) condenser flooding with excess working fluid (excess-liquid heat pipe), (3) vapor flow control (vapor-flow modulated heat pipe), and (4) liquid flow control (liquid-flow modulated heat pipe).
The Hudson Products Corporation is currently marketing a heat pipe air heater for application to heat recovery in boilers. Gas-loaded variable conductance heat pipes have been proposed for use in Hudson's air heater. The gas-loaded heat pipe would be used as a passive technique for controlling surface temperatures to minimize or eliminate acid condensation on heat pipe surfaces. Work that was done in this connection, showed that gas-loaded heat pipes could be used in this application but for a typical 1.77 inch inside diameter heat pipe, a 9.7 foot long gas reservoir would be needed. This adds a significant length to the heat pipe.
U.S. Pat. No. 3,812,905 to Hamerdinger, et al discloses a heat pipe which employs a magnetic working fluid and a magnetizable member to form a hermetic seal in the wick and vapor passage areas of the heat pipe. In this way, the condenser length is variable so as to provide heat pipe control operating temperature and pressure by positioning the magnetizable member to some position along the length inside the heat pipe. Thus, the effective length of the condenser portion of the heat pipe is controlled.
U.S. Pat. No. 3,933,198 to Hara, et al relates to a heat transfer device (which includes heat pipes). This reference discloses the use of a movable plug which varies the pressure of a noncondensable gas in the vessel. A modified embodiment has a flexible relatively small vessel in the heat transfer device. The vessel is charged with some type of fluid from outside the vessel to vary the volume of the vessel, thus varying the pressure of the noncondensable gas.
U.S. Pat. No. 4,403,651 to Groke and U.S. Pat. No. 4,345,642 to Ernst, et al illustrate the state of the art concerning heat pipes.
U.S. Pat. No. 4,403,651 discloses a heat pipe with a hermetically sealed residual gas collector vessel provided in the inner chamber of the heat pipe. A narrow tube transfers any condensate to the collector vessel.
Of further interest is U.S. Pat. No. 3,614,981 to Coleman, et al which also discloses a restriction within the heat pipe.